Epimerisation of saccharides

ABSTRACT

The present invention relates to a process for an epimerization of a saccharide in a microdevice consisting of a network of micron-sized channels in presence of molybdenum containing catalyst. It further relates to the use of a microdevice consisting of a network of micron-sized channels for the epimerization reaction of saccharides and the oligomerization of the thus obtained epimerized saccharide, preferably into manno-oligosaccharides.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of international applicationPCT/EP2011/000550, filed Feb. 7, 2011, which application claims priorityto European Application 10001498.4, filed Feb. 15, 2010, whichapplications are hereby incorporated by reference herein in theirentirety.

FIELD OF THE INVENTION

The present invention relates to a process for epimerization and/oroligomerisation of saccharides, preferably for the preparation ofmannose, and/or manno-oligomers, by using a microdevice consisting of anetwork of micron-sized channels.

BACKGROUND OF THE INVENTION

In order to continually improve physical standards of living for greaternumber of people, it is necessary to achieve more results with fewerresources. Therefore there is the tendency towards building andmanufacturing smaller-scale products due to the desire for sizeefficiency. Most recently, scientists have learned that not onlyelectronic devices, but also mechanical devices, may be miniaturized andbatch-fabricated, promising the same benefits to the mechanical world asintegrated circuit technology has given to the electronic world.

Saccharide epimerisation reactions are well known and it is inparticular known that glucose may be epimerised to give an equilibriummixture of glucose and mannose by means of a molybdenum catalyst. Theearliest reference to this reaction is by V. Bilik in Chem. Zvesti, 26,183-186 (1972) while U.S. Pat. No. 4,029,878, published 14 Jun. 1977,contains a description of a process using the catalytic reaction.Examples of suitable molybdenum catalysts given in U.S. Pat. No.4,029,878 include molybdic acid, isopolymolybdic acids,heteropolymolybdic acids and acid salts such as sodium phosphomolybdateand silicomolybdic acid. This patent also describes the possibility ofusing as catalyst an anion exchange resin in which the hydroxyl ionshave been replaced by molybdate ions.

A later Japanese patent JP 55076894 discloses the use of molybdateimmobilised on anion exchange fibers. When activity of themolybdate-anion exchange fibre conjugate diminishes, the epimerisationprocess is stopped and the exhausted catalysator is leached off withalkali. Immobilisation of fresh molybdic acid on the original anionexchange fibre ensures a new active molybdate-anion exchange fiberconjugate.

European Patent 0 400 641 B1 also describes the use of molybdateexchanged anion exchange resin for epimerisation purposes. In thispatent operation parameters are chosen in such a way that a minimalamount of bound molybdenum is leached out during epimerisation.

EP 0 710 501 describes the catalyst regeneration of a supportedmolybdenum catalyst.

Kockritz describes in Applied Catalysis A: General 334 (2008) pages112-118, a rearrangement of glucose to mannose catalysed bypolymer-supported molybdenum catalysts in the liquid phase.

Japanese patent publication (JP 4-368347, published 21 Dec. 1992)describes the use of a supported catalyst on a macroporous, stronglybasic anion exchange resin.

In general, the benefits of miniaturized systems have been recognizedbut there is still a need for further developing the use of thesesystems in reactions for epimerization reactions and/or oligomerisationof saccharides.

SUMMARY OF THE INVENTION

The current invention relates to a process for the epimerisation of asaccharide wherein an aqueous solution containing the saccharide is fedinto a microdevice consisting of a network of micron-sized channels andis contacted with a molybdenum-containing catalyst.

Furthermore the molybdenum-containing catalyst is provided in an aqueoussolution or is supported on an inorganic or organic carrier.

The current invention relates to a process for preparing a mannosecontaining solution, the enrichment of the mannose and a oligomerisationof mannose-containing solutions into manno-oligosaccharides.

The current invention further relates to the use of a microdeviceconsisting of a network of micron-sized channels for epimerisation ofsaccharides.

The current invention further relates to a micron-sized channel of amicrodevice consisting of a network of micron-sized channels and saidchannel is coated with molybdenum-containing catalyst.

Furthermore, the current invention relates to a molybdenum-containingcatalyst supported on a carrier suitable for application in amicrodevice consisting of a network of micron-sized channels.

Finally it relates to the use of the previously preparedmanno-oligosaccharides into animal feed.

DETAILED DESCRIPTION

The current invention relates to a process for the epimerisation of asaccharide wherein an aqueous solution containing the saccharide is fedinto a microdevice consisting of a network of micron-sized channels andis contacted with a molybdenum-containing catalyst. The contact isoccurring in the microdevice consisting of a network of micron)sizedchannels. Preferably the microdevice is a micro reactor deviceconsisting of a network of micron-sized channels etched into a solidsubstrate.

The saccharide, (=reactants or feedstocks) in the epimerisation reactionis containing at least one aldose or aldose analog. An aldose is acarbohydrate containing an aldehyde group. Those with 4 carbons arecalled tetroses those with 5 carbons are called pentoses, those with 6are called hexoses, those with 7 heptoses and so forth. The tetrosesconsist of erythrose and threose. Included in the pentoses are ribose,arabinose, xylose and lyxose. The hexoses contain allose, altrose,glucose, mannose, gulose, idose, galactose and talose. Although thehexoses as a group, in particular glucose, may be the most important,the epimeric pentoses, ribose and arabinose are also important in thepractice of the invention. A class of aldose analogs consists ofn-deoxy-aldoses such as rhamnose, 6-deoxy-glucose, 4-deoxy-lyxose,5-deoxy-arabinose, 4-deoxy-mannose and 5-deoxy-talose. Another class ofaldose analogs includes aldose esters and ketals, such asglucose-6-acetate, mannose-5,6-dibutyrate, 4,6-O-ethylene-mannose andthe like. Yet another class is that of uronic acids, such as alduronicacids, e.g. glucuronic acid, mannuronic acid, galacturonic acids and thelike. Still other classes of aldose analogs are that of the6-deoxy-6-amino-aldoses, the 4,5 or 6-O-alkyl aldoses and the 4-, 5- or6-deoxy haloaldoses. Preferably the saccharide is glucose.

The concentration of the saccharide is not important in the practice ofthe invention, although as a practical consideration it is advantageousto have the solutions as concentrated as possible consistent withviscosity requirements. The saccharide solution fed into the microdeviceconsisting of a network of micron-sized channels, comprises 10 to 90% byweight dry substance, preferably 15% to 80% by weight, more preferably40% to 70% by weight dry substance most preferably 50% to 60%. Thesaccharide solution can be applied at 35%, 45% and 55%, 65% and 75% drysubstance as well.

The pH at which the epimerisation reaction is effected can have aninfluence on the activity and stability of the molybdenum-containingcatalyst and is in the range of 0.1 to about 8.0, in the range of 0.5 to7, preferably in the range of 0.5 to 6, in the range of 1 to 4, morepreferably in the range of 1 to 3.

The epimerisation reaction is usually performed in a temperature rangebetween about 40° C. and 250° C., preferably from 60 to 180° C., morepreferably from 70 to 150° C. Effective epimerisation can also beobtained at temperatures of 100 to 120° C.

The time over which the epimerisation is conducted will be quitevariable depending upon the reaction temperature, the catalyst amount,the extent of conversion sought and the microdevice consisting of anetwork of micron-sized channels. Consequently the epimerisation willrun for a time sufficient to achieve a commercial acceptable productdistribution. Preferably the reaction time is less than 30 minutes, lessthan 15 minutes, less than 10 minutes, more preferably less than 5minutes, about 5 minutes, about 2.5 minutes, and even most preferablyless than 1 minute.

Microdevices consisting of a network of micron-sized channels (alsoknown as microreactors) are usually defined as miniaturized reactionvessels fabricated at least partially, by methods of microtechnology andprecision engineering. The characteristics dimensions of the internalstructure of microreactor fluid channels (micron-sized channels) canvary substantially, but typically range from the sub-micrometer to thesub-millimeter range. Microreactors most often are designed withmicrochannel architecture. These structures contain a large number ofchannels and each micron-sized channel is used to convert a small amountof material. A number of materials such as silicon, quartz, glass,metals and polymers have been used to construct micro reactors.Depending on the material used, a range of channel micro fabricationmethods such as photolithography, hot embossing, powder blasting,injection moulding and laser micro forming are available. P.D.I Fletcherprovides in Tetrahedron report 609 (Tetr. 58 (2002), 4735-4757) a reviewof microreactors, the principles and applications in organic synthesis.

The benefits of miniaturized systems, designed with dimensions similarto microreactors (microdevices), compared to a large scale processinclude but are not limited to the following advantages, large scalebatch process can be replaced by a continuous flow process, smallerdevices need less space, fewer materials, less energy and often shorterresponse times and system performance is enhanced by decreasing thecomponent size, which allows integration of a multitude of smallfunctional elements. Consequently, microreactors (microdevices)significantly intensify heat transfer, mass transport, and diffusionalflux per unit volume or unit area. The current invention benefits fromincreased reaction speed, high conversion rate and/or reduced diminutionof the catalyst activity (=low leaching) by applying a microdeviceconsisting of a network of micron-sized channels.

Typical thickness of the fluid layer in a microreactor can be set to fewtens of micrometers (typically from about 10 μm to about 1 mm) in whichdiffusion plays a major role in the mass/heat transfer process.Preferred typical dimensions are in the range of 10 to 300 μm. Due to ashort diffusional distance, the time for a reactant molecule to diffusethrough the interface to react with other molecular species is reducedto milliseconds and in some cases to nanoseconds. Therefore theconversion rate is significantly enhanced and the chemical reactionprocess appears to be more efficient.

The epimerisation reaction is effected by any molybdenum-containingcatalyst of Mo(VI) whose solubility in aqueous solution is at least 100ppm at some point within the pH range of 0.1 to 8.0. Examples ofsuitable molybdenum catalysts are given in U.S. Pat. No. 4,029,878 andinclude molybdic acid, isopolymolybdic acids, heteropolymolybdic acidsand acid salts such as sodium phosphomolybdate and silicomolybdic acid.Molybdate salts, i.e. salts of MoO₄ dianion are most commonly used inepimerisation reactions of saccharides and they include molybdate saltsof sodium, potassium, lithium, calcium, strontium, zinc, iron(II),magnesium, ammonium and barium and the like. Organo-metallic molybdatecomplexes such as molybdenum(VI) oxide bis(2,4-pentanedionate), also maybe used in the practice of this invention as well as molybdenum trioxidewhich usually is considered a water-insoluble material but whosesolubility is sufficient to satisfy the criteria articulated above. Theepimerisation can in fact be affected by any molybdenum species insolution or supported on an inorganic or organic carrier where it isplaced on an exchangeable site convertible to a molybdenum (VI) oxyanion.

A typical example of a suitable organic carrier is an anion exchangeresin, and especially a strong anion exchange resin which has beenexchanged with molybdate over a particular pH range. The anion exchangeresin may be of the gel or macroreticular type, with its particularnature not being of special significance.

The supported catalyst may be prepared by contacting the support with anaqueous solution of the molybdenum compound suitably at ambienttemperature for a period of time sufficient to achieve the desiredloading of the catalyst on the support eg. up to 12 hours. The pH of thesolution of the molybdenum compound in contact with the support isadvantageously in the range 0.5 to 7, preferably 1.0 to 5.5. Thepreferred loading of the molybdenum compound catalyst on the supportwill vary from support to support but may be determined by simpleexperiment. Too high a loading for a given support should be avoidedbecause of the disadvantage of an increased leaching of molybdenum fromthe support into the solution during the epimerisation reaction.

The supported organic carrier can be applied in the microreactor suchthat a heterogeneous mixture is provided into the microreactor. The sizeof the resin beads will be adapted to the size of the micron-sizedchannels of the microdevice consisting of a network of micron-sizedchannels. Alternatively at least one micron-sized channel is supportedwith, coated with, or equipped with the molybdenum-containing catalyst.

The inorganic carrier is selected such that the molybdenum catalyst isincorporated into, supported on, coated on, attached to the carrier inorder to allow a smooth epimerisation reaction and yet a low leaching ofthe molybdenum is occurring during the epimerisation reaction.Furthermore, the inorganic carrier allows a type of attachment to atleast one micron-sized channel of the microdevice consisting of anetwork of micron-sized channels. Preferably more than one, morepreferably several or all micron-sized channels of the microdeviceconsisting of a network of micron-sized channels are supported with,coated with, or equipped with the molybdenum-containing catalyst.

The current invention further relates to a molybdenum-containingcatalyst supported on a carrier suitable for application in microdeviceconsisting of a network of micron-sized channels.

The process of the current invention can run in batch,semi-continuously, pulse or continuously, preferably continuously. Theselectivity of the epimerisation reaction can be further increased byadding other components such as boron compounds, being provided inaqueous solution or supported on a carrier, which in turn can beattached to, incorporated into, supported on (=micron-channel is coatedwith) at least one micron-sized-channel of the microdevice consisting ofa network of micron-sized channels.

Furthermore, the selectivity of the epimerisation reaction can beaffected by supplying the saccharide in an aqueous solution or anon-aqueous solution, such as alcohols and/or ethers. Suitable alcoholsand ethers are methanol, ethanol, glycerol, ethylene glycol or ethyleneglycol ether and mixtures thereof, either alone or in combination withwater.

In a preferred embodiment, the process of the current inventioncomprises the use of glucose solutions as the saccharide. The aqueoussolution of the glucose is passed through a microdevice consisting of anetwork of micron-sized channels and which is containing amolybdenum-containing catalyst. The epimerisation can be homogeneouslycatalysed (i.e. the molybdenum-containing catalyst is provided insolution), preferably heterogeneously catalysed whereby themolybdenum-containing catalyst is attached to, incorporated intosupported on (=micron-channel is coated with) at least onemicron-sized-channel of a microdevice or whereby themolybdenum-containing catalyst is provided on a carrier that in turn canbe attached to, incorporated into at least one micron-sized-channel of amicrodevice consisting of a network of micron-sized channels.

Upon finalising the epimerisation reaction in the microdevice consistingof a network of micron-sized channels, the obtained mannose containingsolution is collected.

Although not required by the current invention, the mannose containingsolution may optionally be subjected to conventional ion exchangechromatography.

The reaction (=epimerized saccharide) solution (is mannose containingsolution) or optionally the solution obtained after the ion exchangetreatment is then subjected to liquid chromatography so as to provide atleast one fraction which is enriched in mannose content. Optionallymannose is isolated from this enriched mannose solution.

Furthermore, the current invention further relates to a process whereinthe mannose containing solution, the enriched mannose containingsolution, the isolated mannose or mixture of two or more thereof areoligomerised to a manno-oligosaccharide containing composition byapplying a microdevice consisting of a network of micron-sized channelsand in presence of an acidifying catalyst.

These acidifying catalysts comprise one or more mineral acids such ashydrochloric acid, sulphuric acid, sulphurous acid, thiosulfuric acid,dithionic acid, pyrosulfuric acid, selenic acid, selenious acid,phosphorous acid, boric acid, perchloric acid, hypochlorous acid,hypobromic acid, hydroiodic acid, silicic acid, acidic alkali metal oralkaline earth metal salts of the above acids such as sodium bisulphateand sodium bisulfite, or mixture of these acids (and/or acidic alkali oralkaline earth metals salts) with phospohoric acids, or acids which areallowable for consumption in order to reduce the otherwise necessarycontrols and costs to check for the presence of and, if necessary,remove the catalyst acids from the final product. In particular, theedible acids (food grade acids) are phosphoric acid, citric acid, malicacid, succinic acid, adipic acid, gluconic acid, tartaric acid, fumaricacid and mixtures thereof. Particularly preferred are citric acid and/orphosphoric acid. The amount of acid to be used as catalyst should bebelow 15 weight % relative to the amount of saccharide starting materialused in the oligomerisation reaction. Preferably, this amount should beclearly below this level, such as e.g. at most 12 weight %, at most 10weight %. The addition of the acid can be done in any vessel but mightoccur in the microdevice consisting of a network of micron-sizedchannels as well. Before injecting the carbohydrate containing mixturethrough the microdevice consisting of a network of micron-sizedchannels, the mixture can be heated by using a micro-heat-exchangerand/or microwaves or any other suitable heating device.

The temperature of the oligomerisation is from 100° C. to 350° C.,preferably from 150° C. to 250° C., more preferably from 180° C. to 200°C.

Before collecting the oligomers, the product can be cooled by using amicro heat exchanger.

In oligomerisation reactions, one is usually interested in obtaining aproduct of specific molecular weight or a range of products withspecific molecular weights, since the properties of the oligomers willusually be dependent on molecular weight. Molecular weights higher orlower than the desired weights are equally undesirable. Since the degreeof oligomerisation is a function of reaction time, the desired molecularweight can be obtained by quenching the reaction at the appropriatetime. It has been seen that by applying a microdevice consisting of anetwork of micron-sized channels, the reaction time which usually takesat least 1 to 2 hours, even up to 6 hours, can be reduced to less than30 minutes, preferably less than 15 minutes, preferably less than 10minutes, preferably less than 5 minutes.

Manno-oligosaccharides prepared according to the process of the currentinvention are oligosaccharides having a repeating saccharide entity(predominantly mannose) of at least 2 and up to 20. Themanno-oligosaccharides may further comprise alpha and beta linkages,linear and/or branched, as well as 1,2-, 1,3-, 1,4- and 1,6-linkages andmixtures thereof.

The current invention further relates to the use of a microdeviceconsisting of a network of micron-sized channels for epimerisationreactions of saccharides, preferably for the epimerisation of glucoseinto mannose.

Furthermore, the current invention relates to a (at least one)micron-sized-channel of a microdevice consisting of a network ofmicron-sized channels and said micron-sized channel is supported with,coated with, incorporated with, or equipped with molybdenum containingcatalyst. Consequently, a microdevice consisting of a network ofmicron-sized channels wherein at least one micron-sized-channel issupported with, coated with, incorporated with or equipped withmolybdenum containing catalyst is part of this current invention aswell. Preferably more than one, more preferably several micron-sizedchannels, most preferably most or all of the micron-sized channels ofthe microdevice consisting of a network of micron-sized channels aresupported with, coated with, incorporated with, or equipped withmolybdenum-containing catalyst in order to further improve theefficiency and selectivity of the epimerisation reaction.

The current invention further relates to the use of the previouslyprepared manno-oligosaccharides in animal feed. These newly preparedmanno-oligosaccharides can act as inhibitors of pathogen adhesion tomammalian cells, especially mammalian gut cells. Thesemanno-oligosaccharides may be provided as part of a meal and may benutritionally completed with vitamins, minerals, trace elements as wellas nitrogen, carbohydrate and fatty acid sources.

The invention will hereunder be illustrated in the form of the followingexamples.

EXAMPLES Example 1

Crystalline Dextrose monohydrate (Cargill C*Dex 02001) was solubilisedin water to prepare a glucose solution at 50% solids content. Ammoniumheptamolybdate (Merck, Art. 1182, Lot no.: 2522795) was added in anamount of 0.2 g per 100 g glucose dry substance. The resulting solutionwas pumped at a rate of 0.5 ml/min to a micro heat exchanger(Kreuzstromreaktormodul 1694-X-19.0, KIT, IMVT) which increased theproduct temperature to 150° C. The residence time in the micro reactorwas 5 minutes. The reaction solution mass was then conveyed continuouslyinto a second micro heat exchanger (Kreuzströmer 678-K-1.3, KIT, IMVT)where the product was cooled down to ambient temperature. The solutionleft the micro heat exchanger via a pressure holding valve which keptthe pressure in the micro reactor system at ca. 4.8 bar. The HPLCanalysis (ISO 10504:1998-10, using a Pb-column (Biorad HPX87P) insteadof the mentioned Ca-column) showed a Mannose content of the finalsolution of 30% based on the total carbohydrate content.

Example 2

Crystalline Dextrose monohydrate (Cargill C*Dex 02001) was solubilisedin water to prepare a glucose solution at 50% solids content. Ammoniumheptamolybdate (Merck, Art. 1182, Lot no.: 2522795) was added in anamount of 0.2 g per 100 g glucose dry substance. The resulting solutionwas pumped at a rate of 1 ml/min to a micro heat exchanger(Kreuzstromreaktormodul 1694-X-19.0, KIT, IMVT) which increased theproduct temperature to 150° C. The residence time in the micro reactorwas 2.5 minutes. The reaction solution mass was then conveyedcontinuously into a second micro heat exchanger (Kreuzströmer 678-K-1.3,KIT, IMVT) where the product was cooled down to ambient temperature. Thesolution left the micro heat exchanger via a pressure holding valvewhich kept the pressure in the micro reactor system at ca. 4.8 bar. TheHPLC analysis (ISO 10504:1998-10, using a Pb-column (Biorad HPX87P)instead of the mentioned Ca-column) showed a Mannose content of thefinal solution of 26% based on the total carbohydrate content.

The invention claimed is:
 1. A process for the epimerisation of asaccharide, the process comprising: a) providing a molybdenum-containingcatalyst that is fixed onto an inorganic carrier; b) applying themolybdenum-containing catalyst into a microdevice, wherein themicrodevice consists of a network of micron-sized channels and themolybdenum-containing catalyst is attached to, incorporated into, orsupported on at least one micron-sized channel of the microdevice; andc) feeding an aqueous solution containing the saccharide into themicrodevice, thereby contacting the aqueous solution with amolybdenum-containing catalyst to provide an epimerized saccharide. 2.The process of claim 1, wherein the epimerisation reaction is run forless than about 5 minutes.
 3. The process of claim 1, wherein theepimerisation reaction is run for less than about 2.5 minutes.
 4. Theprocess of claim 1, wherein the epimerisation reaction is run for lessthan about 1 minute.
 5. The process of claim 1, wherein the saccharideis glucose and the epimerized saccharide is mannose.
 6. The process ofclaim 5, further comprising: d) oligomerizing the epimerized saccharidein a microdevice consisting of a network of micron-sized channels toprovide manno-oligosaccharides.
 7. The process of claim 5, furthercomprising: d) oligomerizing the epimerized saccharide in a microdeviceconsisting of a network of micron-sized channels in the presence of anacidifying catalyst to provide manno-oligosaccharides.
 8. The process ofclaim 5, further comprising: e) feeding the epimerizedsaccharide-containing solution into a microdevice consisting of anetwork of micron-sized channels and in the presence of an acidifyingcatalyst to allow for oligomerisation of the epimerizedsaccharide-containing solution into manno-oligosaccharides.
 9. Theprocess of claim 5, further comprising: d) enriching mannose of theepimerized saccharide-containing solution to provide an enriched-mannosesolution.
 10. The process of claim 9, further comprising: e) feeding theenriched mannose solution or a mixture of the enriched mannose solutionwith the epimerized saccharide-containing solution into a microdeviceconsisting of a network of micron-sized channels and in the presence ofan acidifying catalyst to allow for oligomerisation of the enrichedmannose solution or a mixture of the enriched mannose solution with theepimerized saccharide-containing solution into manno-oligosaccharides.11. The process of claim 9, further comprising: f) isolating mannosefrom the enriched-mannose solution.
 12. The process of claim 11, furthercomprising: g) feeding the mannose-containing solution, the enrichedmannose solution, the isolated mannose, or a mixture of two or morethereof into a microdevice consisting of a network of micron-sizedchannels and in the presence of an acidifying catalyst to allow foroligomerisation of the mannose-containing solution, the enriched mannosesolution, the isolated mannose, or a mixture of two or more thereof intomanno-oligosaccharides.